An incredibly rare phenomenon, known as a single top quark, has been observed as part of the LHC experiment, paving the way for scientists to gain a deeper understanding of the fundamental forces of nature.
The Large Hadron Collider (LHC) observed this single top quark along with W and Z bosons, an extremely rare process that happens only once every trillion proton collisions.
Finding this event in the LHC data is like searching for a needle in a haystack the size of an Olympic stadium.
Pointing to new physics beyond the Standard Model
The creation of a single top quark, a W boson and a Z boson, known as tWZ production, opens up a new window for understanding the fundamental forces of nature.
By closely studying tWZ production, physicists can investigate how the top quark interacts with the electroweak force, which is carried by the W and Z bosons.
Furthermore, the top quark is the heaviest known fundamental particle, meaning that it has the strongest interaction with the Higgs field, so studying the tWZ process could give us a deeper understanding of the Higgs mechanism.
It could also point us to signs of new phenomena and physics beyond the Standard Model.
Advanced analysis techniques for identifying the tWZ production
However, observing tWZ production is not easy. Not only is it one of the rarest Standard Model processes that can currently be observed at the LHC, but it is also very complex to analyse.
This process resembles another one known as ttZ production, in which a top and an anti-top quark are produced along with a Z boson. This ttZ production occurs about seven times more frequently than tWZ production, which means that there is a significant amount of background noise that researchers must identify and account for.
Alberto Belvedere, a researcher with the CMS collaboration at DESY, explained: “Because of its rarity and its similarity with the ttZ process, observing tWZ production requires advanced analysis techniques involving state-of-the-art machine learning.”
Using their machine learning algorithm, the researchers were able to separate the signal from tWZ production from the background data.
Uncovering nature’s most elusive secrets with the LHC
The CMS collaboration found that the rate of tWZ production was slightly higher than predicted by the theory.
Future data and analysis will clarify whether this is just a statistical fluctuation or whether it could be the first hint of something beyond the known laws of physics.
“If there are unknown interactions or particles involved, the observed deviation between the measured rate of tWZ production and the prediction would rapidly become larger with increasing energies of the outgoing particles, an effect that is unique to the tWZ process”, stated Roman Kogler, a researcher with the CMS collaboration at DESY.
For now, the CMS collaboration has observed a phenomenon so rare that it occurs only once every trillion proton-proton collisions.
This rare single top quark phenomenon is yet another reminder of the LHC’s ability to uncover nature’s most elusive secrets as part of its experiments.
